Publication appeared in Physical Review Applied


Our Numerical Investigation of Photon-Pair Generation in Periodically Poled MTiOXO4 (M=K, Rb, Cs; X=P, As) appeared in Physical Review Applied.

We present a detailed numerical investigation of five nonlinear materials and their properties regarding photon-pair creation using parametric down-conversion. Periodic poling of ferroelectric nonlinear materials is a convenient way to generate collinearly propagating photon pairs. Most applications and experiments use the well-known potassium titanyl phosphate (KTiOPO4, PPKTP) and lithium niobate (LiNbO3, PPLN) crystals for this purpose. We provide a profound discussion on the family of KTP-isomorphic nonlinear materials, including KTP itself but also the much less common CsTiOAsO4, KTiOAsO4, RbTiOAsO4, and RbTiOPO4. We discuss the way in which these crystals can be used for the creation of spectrally pure down-conversion states and the generation of crystal-intrinsic polarization and frequency entanglement. The investigation of the new materials discloses an entirely different range of promising experimental setups, in some cases even outperforming the established materials PPLN and PPKTP.


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Purity vs Gaussian-pulse duration τ and crystal length L. The example corresponds to the down-conversion 791  nm(o)→1582  nm(o)+1582  nm(e) in PPKTP. (Insets) The joint spectral intensity distribution corresponding to particular pairs of τ and L. The white curves in the insets illustrate the spectral intensity distribution of the signal (the horizontal axis) and the idler (the vertical axis). Although signal and idler are spectrally indistinguishable for any pair of τ and L’s, a high intrinsic purity (i.e., frequency-uncorrelated daughter photons) can be obtained only by a mutual matching of the two. A short-pulsed (and therefore broadband) laser pumping a long crystal will generate frequency-correlated spectra (the left inset); a long-pulsed (hence, narrow band) laser in a short crystal will produce an anticorrelated signal and idler (the right inset). The top and bottom insets represent spectrally uncorrelated SPDC states, achieved by an appropriate matching of pulse duration and crystal length.